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United States Patent |
6,047,767
|
Bodhaine
,   et al.
|
April 11, 2000
|
Heat exchanger
Abstract
A heat exchanger is disclosed having a first chamber, a second chamber
positioned inside the first chamber, and a third chamber positioned inside
the second chamber. The first, second, and third chambers are in coaxial
alignment. A first portion of a first helical tube is positioned inside
the second chamber and a second portion of the first helical tube is
positioned inside the third chamber and a second helical tube is
positioned inside the first chamber. The heat exchanger heats a cryogenic
liquid to a gas phase using at least three different heat transfer fluids
in one contained unit without mixing any of the fluids in the exchanger.
Inventors:
|
Bodhaine; Jim (Houston, TX);
Hassanein; Hany E. (Houston, TX)
|
Assignee:
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Vita International, Inc. (Houston, TX)
|
Appl. No.:
|
063603 |
Filed:
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April 21, 1998 |
Current U.S. Class: |
165/141; 165/156; 165/163 |
Intern'l Class: |
F28D 007/10 |
Field of Search: |
165/140,141,154,155,156,163
|
References Cited
U.S. Patent Documents
1095165 | Apr., 1914 | Ockel | 165/140.
|
1114924 | Oct., 1914 | Skinner | 165/141.
|
1279135 | Sep., 1918 | Manville | 165/140.
|
1526320 | Feb., 1925 | Cook | 165/140.
|
1922149 | Aug., 1933 | Baumann | 165/156.
|
3131553 | May., 1964 | Ross | 165/140.
|
4197712 | Apr., 1980 | Zwick.
| |
4241043 | Dec., 1980 | Hetzel | 165/141.
|
4290271 | Sep., 1981 | Granger.
| |
4420942 | Dec., 1983 | Davis.
| |
4576005 | Mar., 1986 | Force.
| |
4586338 | May., 1986 | Barrett.
| |
4599868 | Jul., 1986 | Lutjens.
| |
4819454 | Apr., 1989 | Brigham.
| |
4899544 | Feb., 1990 | Boyd.
| |
5046548 | Sep., 1991 | Tilly | 165/140.
|
5095709 | Mar., 1992 | Billiot.
| |
5228505 | Jul., 1993 | Dempsey | 165/140.
|
5339654 | Aug., 1994 | Cook et al. | 165/163.
|
5551242 | Sep., 1996 | Loesch.
| |
5713216 | Feb., 1998 | Erickson | 165/163.
|
Foreign Patent Documents |
0 805 303 | Nov., 1997 | EP.
| |
1 192 240 | Oct., 1959 | FR.
| |
2 479 436 | Oct., 1981 | FR.
| |
2 660 056 | Sep., 1991 | FR.
| |
1 936 782 | Feb., 1970 | DE.
| |
16 01 222 | Jul., 1970 | DE.
| |
27 08 337 | Aug., 1978 | DE.
| |
31 17 431 | Mar., 1982 | DE.
| |
82 00053 | Jan., 1982 | WO.
| |
Other References
Georgiev, Kovatchev: "Multichannel low Temperature Heat Exchanger";
Cryogenics, vol. 14, No. 1; Jan. 1974 (1974-01), pp. 25-28.
|
Primary Examiner: Leo; Leonard
Attorney, Agent or Firm: Paula D. Morris & Associates P.C., Seal; Cynthia G.
Claims
We claim:
1. A heat exchanger comprising:
a first chamber having at least one inlet;
a second chamber having at least one inlet, wherein the second chamber is
positioned inside the first chamber;
a third chamber having at least one inlet, wherein the third chamber is
positioned inside the second chamber, wherein said first, second, and
third chambers are in coaxial alignment;
a first helical tube having an inlet, a first portion positioned inside the
second chamber and a second portion positioned inside the third chamber;
and
a second helical tube having an inlet, wherein the second helical tube is
positioned inside the first chamber.
2. The heat exchanger of claim 1, wherein the first tube has a first fluid
flow therethrough, the second tube has a second fluid flow therethrough,
the second chamber has a third fluid flow therethrough that flows to the
first chamber and the third chamber has a fourth fluid flow therethrough,
wherein the first, second, third, and fourth fluid flows do not mix.
3. The heat exchanger of claim 2, wherein the first fluid flow through the
first portion of the first tube is in a counter-flow arrangement with the
third fluid flow in the second chamber.
4. The heat exchanger of claim 2, wherein the first fluid flow through the
second portion of the first tube is in a counter-flow arrangement with the
fluid flow in the third chamber.
5. The heat exchanger of claim 2, wherein the second fluid flow through the
second tube is in a counter-flow arrangement with the fluid flow in the
first chamber.
6. The heat exchanger of claim 1, wherein the first, second and third
chambers are generally cylindrical.
7. The heat exchanger of claim 1, wherein the second chamber is made from a
heat conducting material.
8. The heat exchanger of claim 1, wherein the third chamber is made from a
heat conducting material.
9. The heat exchanger of claim 2, further comprising a third helical tube
having an inlet positioned inside the first chamber in parallel with the
second helical tube.
10. The heat exchanger of claim 9, wherein the third helical tube has a
fifth fluid flow therethrough, wherein the fifth fluid flow is in a
counter-flow relationship with the fluid flow inside the first chamber.
11. The heat exchanger of claim 1, further comprising a first spiral fin
positioned inside the first chamber, wherein at least some of the turns of
the spiral fins are positioned between each turn of the second helical
tube.
12. The heat exchanger of claim 1, further comprising a second spiral fin
positioned inside the second chamber, wherein each turn of the second
spiral fin is positioned between at least some of the turns of the first
portion of the first helical tube.
13. The heat exchanger of claim 1, further comprising a cylindrical core
positioned inside the third chamber.
14. The heat exchanger of claim 13, further comprising spiral fins
positioned on an exterior surface of the cylindrical core.
15. A heat exchanger comprising,
a plurality of coaxially aligned chambers for providing radial, thermal
heat transfer between four separately contained fluids,
a first helical tube having an inlet within at least one of the chambers
and a second helical tube having an inlet within one of the chambers,
wherein the plurality of chambers includes
a first chamber having at least one inlet;
a second chamber having at least one inlet, positioned inside the first
chamber;
a third chamber inside the second chamber, having at least one inlet;
wherein the first helical tube has a first portion positioned inside the
second chamber and a second portion positioned inside the third chamber;
and
the second helical tube is positioned inside the first chamber.
16. The heat exchanger of claim 15, wherein the first tube has a first
fluid flow therethrough, the second tube has a second fluid flow
therethrough, the second chamber has a third fluid flow therethrough that
flows to the first chamber and the third chamber has a fourth fluid flow
therethrough.
17. The heat exchanger of claim 16, wherein,
the first fluid flow is in heat exchange relation with the third fluid flow
within the second chamber and the first fluid flow is in heat exchange
relation the fourth fluid flow within the third chamber; and
the second fluid flow is in heat exchange relation with the third fluid
flow in the first chamber.
18. The heat exchanger of claim 17, wherein
the third fluid and the first fluid flow are in a counter-flow relationship
in the second chamber,
the third fluid and the second fluid flow are in a counter-flow
relationship in the first chamber, and
the fourth fluid flow and the first fluid flow are in a counter-flow
relationship in the third chamber.
19. The heat exchanger of claim 15, wherein the first, second and third
chambers are generally cylindrical.
Description
FIELD OF THE INVENTION
This invention relates to a multiphase heat exchanger that provides radial
thermal heat transfer between a plurality of individually contained
fluids.
BACKGROUND OF THE RELATED ARTS
Numerous operations are performed on oil and gas wells which require large
volumes of nitrogen gas or other cryogenic fluids. These operations may be
performed on both onshore and offshore wells. Such operations include foam
fracturing operations, acidizing services, jetting down the tubing or down
the tubing-casing annulus, nitrogen cushions for drill stem testing,
pressure testing, insulation of the tubing-casing annulus to prevent such
problems as paraffin precipitation, jetting with proppant for perforating
and cutting operations, reduction of density of well workover fluids,
displacement of well fluid from tubing during gun perforation operations
to prevent excess hydrostatic pressure in the hole from pushing
perforation debris into the formation, placing corrosion inhibitors by
misting the inhibitor with nitrogen, extinguishing well fires, and other
operations. Other operations that require cryogenic fluids at an ambient
temperature include pipeline and vessel purging operations and refinery
operations such as, recharging catalysts.
Nitrogen is typically stored in its liquid state because of the volume used
however, liquid nitrogen will damage most carbon steel pipes used in oil
and gas wells. Thus, various heating systems have been developed to raise
the nitrogen to an ambient temperature. Typically, 185 BTUs per pound of
nitrogen are required to heat the nitrogen to an ambient temperatures of
70.degree. F.
One particular such operation is the fracturing of a subsurface formation
of the well by pumping a fluid under very high pressure into the
formation. The fracturing fluid which is pumped into the well often
comprises a foamed gel which is produced by the use of nitrogen gas. The
nitrogen for the foam fracturing operation is generally stored in a fluid
form at temperatures of approximately -320.degree. F.
At pressures encountered in these foam fracturing operations, the nitrogen
changes state from a liquid to a gas at approximately -200.degree. F. It
is, therefore, desirable to heat up the nitrogen gas to a superheated
state so that the foam fracturing fluid being pumped down the well will be
at an essentially ambient temperature. This is because of the numerous
adverse affects upon mechanical equipment of very low temperature which
would otherwise be presented by the nitrogen foam.
With regard to land based wells, the nitrogen heating equipment generally
includes open flame heaters. A problem is however, presented when
performing foam fracturing operations on offshore wells. For safety and
environmental reasons, open flames are generally not allowed on an
offshore drilling platform. Therefore, it is necessary to provide a heater
for the nitrogen which does not have an open flame.
Such flameless nitrogen heaters have previously been provided by utilizing
the heat generated by an internal combustion engine and mechanical
components driven thereby to heat a coolant fluid which transferred that
heat to the nitrogen through a coolant fluid-to-nitrogen heat exchanger.
Numerous problems are encountered with prior art devices mainly because of
the use of air as a heat transfer medium. Air is a notoriously poor heat
transfer medium as compared to a liquid and the use of ambient air causes
the system to be dependent upon ambient air conditions for proper
operation. Additionally, due to the large bulky nature of the plenum
chamber required for the use of air as a heat transfer medium, the air
systems are typically very bulky and heavy. Therefore, there is a need for
a flameless nitrogen unit that is compact in size, efficient in the heat
transfer process, and economical.
SUMMARY OF THE INVENTION
The present invention provides a heat exchanger that collects heat from
three sources generated by a drive system using an internal combustion
engine and uses the heat to warm a fluid stream. The heat exchanger has
three preferably cylindrical chambers one inside the other in coaxial
alignment. The second chamber is positioned inside the first, and the
third chamber is inside the second. Helical tubes are positioned inside
the chambers to carry fluids for the heat exchange process. A first
portion of a first helical tube is positioned inside the second chamber,
and the second portion of the first helical tube is positioned in the
third chamber. The second chamber has a hole in the wall to allow the
passage of the second portion of the first tube into the third chamber. A
second helical tube is positioned inside the first chamber.
Preferably, the first tube has a first fluid flow therethrough such as
nitrogen or some other cryogenic fluid. The second tube has a second fluid
flow therethrough, such as hydraulic fluid from the drive system. The
second chamber has a third fluid flow therethrough, such as engine
coolant, that also flows through the first chamber. Finally, the third
chamber has a fourth fluid flow therethrough, such as exhaust from the
engine. Preferably, the walls of the second and third chambers are made of
a heat conducting material such as stainless steel or copper, so that the
fluids flowing therethrough can benefit from radial heat transfer from one
chamber to the next.
Alternatively, a third helical tube may be positioned inside the first
chamber in parallel with the second helical tube. The third helical tube
has a fifth fluid flow therethrough such as hydraulic fluid from the
casing of the various pumps used in the drive system. In addition, the
fifth fluid flow is preferably in a counter-flow relationship with the
fluid flow inside the first chamber.
In a preferred embodiment, all of the fluids traveling through the heat
exchanger are in a counter-flow relationship, such that, i.) the first
fluid flow through the first portion of the first tube is in a
counter-flow arrangement with the third fluid flow in the second chamber,
ii.) the first fluid flow through the second portion of the first tube is
in a counter-flow arrangement with the fluid flow in the third chamber,
and iii) the second fluid flow through the second tube is in a
counter-flow arrangement with the fluid flow in the first chamber.
In order to maximize the available surface area, the individual chambers of
the heat exchanger may be equipped with spiral fins. The fins are
positioned such that they spiral in the same orientation as the helical
tubes within the chambers and they are positioned between the turns of the
helical tubes. The spiral effect of the fins causes the fluid flow through
the individual chambers to come into contact with all sides of the helical
tubes. The fins can be positioned between each turn or some of the turns
of the helical tubes.
The fourth fluid flow or exhaust passes through the third chamber and
exposes the second portion of the first tube to the heat from the exhaust.
The exhaust then exits through one end of the heat exchanger. In order to
direct the flow from the exhaust, a cylindrical core with spiral fins may
be positioned inside the third chamber. The cylindrical core acts to
reduce sparks from the exhaust and disperse the flow of the exhaust gases
to maximize the surface area of the tube exposed to the exhaust. The unit
may also be equipped with a diffuser at each end and a cone shaped inlet
and outlet for the exhaust gases to reduce engine noise.
Auxiliary pumps may be used to conduct the fluids through the helical tubes
and the coolant through the chambers to compensate for the pressure drop
that is incurred as the fluids flow through the heat exchanger.
In another embodiment, a system is provided for converting a liquid to a
gas. The system includes a liquid source such as liquid nitrogen or other
cryogenic fluid, a drive system including a pump, such as a triplex
nitrogen pump connected to the liquid source. The drive system includes an
internal combustion engine such as a diesel engine from Detroit,
Caterpillar or other commercially available source for driving a hydraulic
pump that provides hydraulic fluid to run a hydraulic motor that drives
the nitrogen pump in addition to other pumps required to transport the
fluids through the system. A heat exchanger is used for providing a first
fluid flow, such as water, from the engine in heat exchange relationship
with the liquid to heat and convert the liquid to a gaseous state. The
heat exchanger further provides a second fluid flow, such as exhaust from
the engine for further heating the cryogenic gas in a heat exchange
relationship. The heat exchanger further provides a third fluid flow, such
as hydraulic fluid from the drive system for heating the first fluid flow.
The heat exchanger is designed such that the first fluid flow, second
fluid flow, third fluid flow do not mix. Preferably, a fourth fluid flow,
comprising casing hydraulic fluid from the pumps and motors, is provided
in a heat exchange relationship with the first fluid flow.
It is preferred that the liquid is nitrogen, the first fluid flow is
substantially water, the second fluid flow is substantially exhaust, and
the third fluid flow is substantially hydraulic fluid, however other
fluids may be substituted to achieve specific heat transfer goals of a
particular system. A valve element may be positioned in communication with
the gas flow as it exits the heat exchanger to control the temperature of
the gas as it exits the heat exchanger. The heat exchanger is designed to
provide maximum heat transfer with minimum heat loss to the atmosphere, to
increase efficiency and lower the cost of providing cryogenic fluids at an
acceptable temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the above recited features and advantages of the present invention
can be understood in detail, a more particular description of the
invention, briefly summarized above, may be had by reference to the
embodiments thereof which are illustrated in the appended drawings. It is
to be noted, however, that the appended drawings illustrate only typical
embodiments of this invention and are therefore not to be considered
limiting of its scope, for the invention may admit to other equally
effective embodiments.
FIG. 1 is a perspective view of the heat exchanger of the present
invention.
FIG. 2 is a cross-sectional view of heat exchanger taken along lines A--A
in FIG. 1.
FIG. 3 is a schematic of a system using the heat exchanger of the present
invention.
FIG. 4 is a perspective view of a cone and diffuser combination of the
present invention.
FIG. 5 is a schematic view of the spiral fins used in the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
One aspect of the present invention provides a heat exchanger that collects
heat through radiant transfer from coolant fluid and exhaust gases and
transfers the heat to the liquid nitrogen. The liquid nitrogen is exposed
to the heat from the engine coolant and is converted to a gas. Once in the
gas phase, the nitrogen is further heated by the exhaust gases and exits
the heat exchanger at a controllable temperature of from 70-150.degree. F.
During the heat transfer process, the engine coolant gives up heat to the
nitrogen and is overcooled by the liquid nitrogen. The overcooled coolant
then travels to the hydraulic chamber and absorbs the heat from the
hydraulic fluids thus reducing the temperature of the hydraulic fluid. The
coolant then travels out of the heat exchanger and back into the engine.
The nitrogen liquid travels in one direction down the heat exchanger
through the second chamber, at the opposite end of the heat exchanger, the
nitrogen, now a gas, reverses direction and travels in the opposite
direction in the third chamber. While in the third chamber, the nitrogen
gas is further warmed by the exhaust stream flowing over the tube carrying
the nitrogen. The nitrogen then exits the heat exchanger for use in the
desired application. The hydraulic fluid is contained in a hydraulic tube
positioned in a first chamber that is filled with circulating coolant that
has been cooled by the liquid nitrogen in a second chamber. Preferably,
all the fluids in this system flow in a counter flow arrangement to
maximize the radiant heat transfer process. The heat exchanger reduces the
amount of heat lost, thereby increasing the efficiency of the heat
transfer, and reducing the size engine required to generate heat. Using a
smaller engine will save space as well as money for the operator.
The temperature of the nitrogen exiting the system is related to the amount
of heat generated by the system. The heat generated by the system can be
balanced by controlling the velocities of fluids flowing through the heat
exchanger. The engine runs at a constant speed, therefore, the coolant
velocity is relatively constant. The nitrogen is delivered through a
hydraulically driven nitrogen pump that is powered by a hydraulic motor,
which is supplied with hydraulic fluid from the engine hydraulic pump. The
nitrogen flow rate dictates the amount of horsepower output required from
the hydraulic motor. A high nitrogen flow rate increases the amount of
hydraulic oil demand from the engine, and increases the horsepower output,
which in turn increases the heat created by the oil, coolant, and exhaust.
In another aspect of the invention, there is provided a heat exchanger that
employs a radial design for transferring heat from several sources into a
fluid stream in one contained unit. The design includes a radial
arrangement of flow tubes and chambers that are self-contained to reduce
heat loss from one heat transfer phase to the next. The unit is designed
to provide multiphase heat transfer using coolant, hydraulic fluid and
exhaust from an external engine to heat liquid nitrogen, cool hydraulic
fluid as well as reduce the temperature of waste exhaust. The heat
exchanger is based on overcooling of the engine coolant by loosing heat to
the liquid nitrogen or other cryogenic fluid, then using the overcooled
coolant to withdraw heat from the hydraulic fluids in an efficient manner.
In addition, cryogenic fluids that are normally vented to atmosphere
during cool downs or pump priming, can be vented directly into the exhaust
stream, further cooling the exhaust and vaporizing the cryogenic fluids
prior to entry to the atmosphere.
In yet another aspect of the present invention, there is provided a
radially designed heat exchanger that muffles the exhaust coming from the
engine. The exhaust is fed through a cone and a diffuser to a cylindrical
core having spiral fins inside the heat exchanger that reduces noise and
acts as a spark arrestor.
For example, the heat exchanger of the present invention may be used to
heat and/or vaporize nitrogen at a rate of 180K scf/h from -320 F. to 115
F. using a 315 HP engine. Currently available systems require a 380 HP
engine to achieve similar results.
FIG. 1 is a perspective view of the heat exchanger 10 of the present
invention. The heat exchanger 10 has a first end 12 and a second end 14. A
liquid nitrogen inlet 16 is located near the first end 12 and a gaseous
nitrogen outlet 22 is located near the first end. The engine coolant
enters the heat exchanger 10 through coolant inlet 24 and exits through
coolant outlet 30. The engine main hydraulic fluid enters through
hydraulic inlet 36 and exits through hydraulic outlet 40. The case
hydraulic fluid enters through inlet 42 and exits through outlet 46. The
engine exhaust enters through exhaust inlet 48 and exits through exhaust
outlet 50. Nitrogen that is normally vented to the atmosphere from various
pumps, can be vented into the exhaust stream through a vent line 58. If
the engine is working very hard and producing exhaust that is too hot to
be vented to the atmosphere, the exhaust can be cooled by injecting a
small amount of liquid nitrogen into the exhaust stream near the second
end of the heat exchanger 10 through inlet 60.
FIG. 2 is a cross-sectional view of heat exchanger 10 taken along lines
A--A. The heat exchanger 10 has a first cylindrical chamber 26, a second
cylindrical chamber 28, and a third cylindrical chamber 32. A first
portion 18 of a first helical tube is positioned inside the second chamber
28 and a second portion 20 of the first helical tube is positioned inside
the third chamber 32. Starting at the first end 12, the nitrogen inlet 16
communicates with the first portion 18 of the first helical tube and the
nitrogen outlet 22 communicates with the second portion 20 of the first
helical tube. Coolant inlet 24 communicates with the second chamber 28
near the second end 14, and coolant outlet 30 communicates with the first
chamber near the second end 14. Hydraulic inlet 36 communicates with the
second helical tube 38 near the second end 14, and hydraulic outlet 40
communicates with the first chamber near the first end 12. The exhaust
inlet 48 communicates with the third chamber 32 near the first end 12, and
the exhaust outlet communicates with the third chamber near the second end
14.
The exhaust chamber 32 may include a cylindrical core 52 for reducing
sparks caused by the exhaust. The cylindrical core 52 may include spiral
fin 54 positioned on the outside of the cylindrical core for dispersing
the exhaust and increasing the surface area of the tubes 20 that are
exposed to the heat from the exhaust, thereby maximizing the heat transfer
therebetween. In addition to the cylindrical core 52, a diffuser 62
equipped with a cone shaped structure, positioned at each end of the third
chamber may be used to reduce the noise from the exhaust.
Each chamber preferably includes a spiral fin that is positioned between
the turns of at least some of the helical tubes to direct fluid flows and
maximize the surface area of the tubes exposed to the fluids. Preferably,
the fins can be made of any commercially available heat transfer medium so
as to not inhibit the heat transfer from the fluid flow to the helical
tubes.
The outer wall of the first chamber 26 can be made from steel, or
preferably a heat transfer material such as brass. The walls of the second
and third chambers may also be made from a heat transfer material such as
steel, copper, brass or mixtures thereof, most preferably, brass, to
maximize the radial heat transfer between the exhaust, hydraulic oil and
the coolant.
FIG. 3 is a schematic of a system using the heat exchanger of the present
invention. A triplex nitrogen pump 74 is used to send nitrogen from a
nitrogen source 70 through conduit 72 to the heat exchanger 10. The pump
74 is driven by a hydraulic motor 86. The engine 76 drives the hydraulic
pump 82 which supplies hydraulic fluid to motor 86 and other hydraulic
motors in the system. The coolant fluid from the engine 76 is pumped into
the heat exchanger 10 through a coolant pump 78 and conduit 80. The case
drain and return hydraulic fluid from a hydraulic pump 82, coolant pump 78
and hydraulic motor 86 are sent to the heat exchanger 10 through via
conduit 84 and exit the heat exchanger through conduit 102 to a hydraulic
fluid source 90. Main hydraulic fluid from hydraulic pump 82, rotary motor
86 is transferred to heat exchanger 10 through conduit 88 and returns to
the hydraulic pump 82 through conduit 89 which completes a closed loop
between hydraulic motor 86 and hydraulic pump 82. The hydraulic pump 82 is
connected to a hydraulic fluid source 90 via conduit 92. The engine
exhaust is transferred to the heat exchanger 10 through conduit 94 and
exits the heat exchanger through conduit 96. Once the coolant exits the
heat exchanger 10, it is transferred to either the engine radiator 98 or
to the water pump in the engine 76. The coolant flow flows from the heat
exchanger 10 through conduit 104 to a thermostatic valve 100 for
regulating flow of the coolant, so that if the coolant temperature is too
high the coolant is transferred to the engine radiator 98.
It is desirable for certain applications that the nitrogen be within a
certain temperature range. In order to achieve a certain temperature
range, a self-controlled tempering valve connected to a nitrogen source
may be used to add liquid nitrogen to the nitrogen gas exiting the system
if the temperature is too high.
FIG. 4 is a perspective view of a cone and diffuser combination that is
positioned on each end of the heat exchanger. Only one cone and one
diffuser is shown for simplicity. The cone 106 is attached, typically with
bolts, to the ends of the heat exchanger, in communication with the
exhaust flow through the heat exchanger. The cone has a diffuser 62 which
consists of a generally flat plate defining holes 110 therethrough. The
cone has an tube 112 extending away from the diffuser 62 for attachment to
the exhaust source at one end of the heat exchanger or for venting the
exhaust to the atmosphere at the other end. The diffuser 62 and cone 106
act to reduce engine noise.
FIG. 5 is a schematic view of the spiral fins used in the present
invention. For clarity, the first chamber 26 is shown in dotted lines and
the helical tube has been removed. The fins 56 are positioned around the
outside of the second chamber 28 for directing the fluid flow through the
first chamber so that the fluid contacts the maximum surface area of the
helical tube passing through the first chamber 26, thus increasing the
heat transfer efficiency of the system.
While the foregoing is directed to the preferred embodiment of the present
invention, other and further embodiments of the invention may be devised
without departing from the basic scope thereof, and the scope thereof is
determined by the claims which follow.
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